03 Fakultät Chemie

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    Eignung von metallorganischen Gerüstverbindungen als stationäre Phase in der Hochleistungsflüssigchromatographie (HPLC)
    (2017) Lieder, Christian; Klemm, Elias (Prof. Dr.-Ing.)
    Anwendung von metallorganischen Gerüstverbindungen als stationäre Phase in der HPLC, Vergleich mit klassischen Silika-Materialien. Synthese der metallorganischen Gerüstverbindungen, Modifizierung. Befüllung chromatographischer Säulen und Gegenüberstellung der Füllmethoden. Methodenentwicklung, Einflüsse auf chromatographische Ergebnisse. Chirale Erkennung, Untersuchung der Wechselwirkungen. Theoretisch chemische Berechnungen der Wechselwirkungen.
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    Chemical ordering and magnetism in face-centered cubic CrCoNi alloy
    (2024) Ghosh, Sheuly; Ueltzen, Katharina; George, Janine; Neugebauer, Jörg; Körmann, Fritz
    The impact of magnetism on chemical ordering in face-centered cubic CrCoNi medium entropy alloy is studied by a combination of ab initio simulations, machine learning potentials, and Monte Carlo simulations. Large magnetic energies are revealed for some mixed L12/L10 type ordered configurations, which are rooted in strong nearest-neighbor magnetic exchange interactions and chemical bonding among the constituent elements. There is a delicate interplay between magnetism and stability of MoPt2 and L12/L10 type of order, which may explain opposing experimental and theoretical findings.
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    Ab initio machine-learning unveils strong anharmonicity in non-Arrhenius self-diffusion of tungsten
    (2025) Zhang, Xi; Divinski, Sergiy V.; Grabowski, Blazej
    The knowledge of diffusion mechanisms in materials is crucial for predicting their high-temperature performance and stability, yet accurately capturing the underlying physics like thermal effects remains challenging. In particular, the origin of the experimentally observed non-Arrhenius diffusion behavior has remained elusive, largely due to the lack of effective computational tools. Here we propose an efficient ab initio framework to compute the Gibbs energy of the transition state in vacancy-mediated diffusion including the relevant thermal excitations at the density-functional-theory level. With the aid of a bespoke machine-learning interatomic potential, the temperature-dependent vacancy formation and migration Gibbs energies of the prototype system body-centered cubic (BCC) tungsten are shown to be strongly affected by anharmonicity. This finding explains the physical origin of the experimentally observed non-Arrhenius behavior of tungsten self-diffusion. A remarkable agreement between the calculated and experimental temperature-dependent self-diffusivity and, in particular, its curvature is revealed. The proposed computational framework is robust and broadly applicable, as evidenced by first tests for a hexagonal close-packed (HCP) multicomponent high-entropy alloy. The successful applications underscore the attainability of an accurate ab initio diffusion database.
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    Molecular modeling of hydrophobic effects in complex biomolecular systems : from simple mixtures to protein-interface aggregation
    (2014) Benson, Sven P.; Pleiss, Jürgen (Prof. Dr.)
    Hydrophobicity is a term commonly used to discuss the formation of molecular structures in aqueous solution, and since water is ubiquitous in cellular systems, it may be applied in virtually every biomolecular context. Hydrophobicity is not a first-principle parameter but an abstract concept to describe the “behavior” of molecules in aqueous environments. The terminology of hydrophobicity is misleading, because it implies repulsion or a lack of attraction between nonpolar groups and water, when in fact attractive interactions persist due to atom dipoles. Although it has long been recognized that the driving force of structure formation in aqueous environments is founded in water’s “narcissism”, i.e., water self-preference, rather than in a general “fear of water”, the term hydrophobicity has established itself ever since Kautzmann related protein stability to hydrophobic interactions. Due to its false implications, hydrophobicity can be a cause of confusion and the culprit of misleading deductions. Presented in this dissertation is the author’s work on the structural and dynamical characterization of hydrophobic effects in biomolecular systems in the broadest sense, whereby molecular systems on three different size scales are covered: binary mixtures of methanol and water, aggregation of triglyceride droplets in aqueous solution and enzymes that interact with triglyceride-water interfaces of large-scale triglyceride aggregates.
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    Toward carbon‐free cathodes for fluoride ion batteries : deconvoluting effects of active material and conductive additive on charging and cyclic stability
    (2025) Aalto, Tommi Hendrik; Talei, Roham; Küster, Kathrin; Schmitz, Guido; Clemens, Oliver
    In this study, conductive, fluorine and antimony codoped tin oxide nanoparticles (FATO‐NPs) are highlighted as a possible alternative for conductive carbon additives in fluoride ion batteries, successfully circumventing oxidative side reactions. Since good cyclability with high and stable discharge capacities is achieved with both types of conductive additive at a high stack pressure of 180 MPa, it is concluded that conductive carbon is well‐suited for high‐voltage fluoride ion batteries, contrary to prior assumptions. However, FATO‐NP‐based cathodes outperform those based on conductive carbon at lower stack pressures of 50 MPa, emphasizing the importance of avoiding carbon fluorination at low stack pressures.
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    Reaktionstechnische Untersuchungen zur oxidativen Veresterung von Methacrolein mit Methanol an Au/NiO-Festbettkatalysatoren
    (2017) Otterstätter, Robin; Klemm, Elias (Prof. Dr.-Ing.)
    Die FISCHER Veresterung erreicht gewöhnlich zufriedenstellende Ausbeuten, wenn aktivierte Carbonsäuren eingesetzt werden. Dies führt zu stöchiometrischen Salzanfällen. Die direkte oxidative Veresterung (DOE) ist eine grüne Alternative zur verbreiteten FISCHER Veresterung. Im Vergleich dazu zieht die DOE Nutzen aus der Verwendung von Sauerstoff als Oxidans, welcher lediglich Wasser als Abfall produziert. Eine heterogene Reaktionsführung erhöht darüberhinaus ihren Vorzug. Ein Ester der in einigen Million Tonnen pro Jahr produziert wird, ist Methylmethacrylat, welches als Polymer eingesetzt wird. Jedoch ist der üblicherweise durchgeführte Produktionspfad sehr teuer und nicht umweltfreundlich: der Acetoncyanhydrin Prozess. Die DOE könnte eine konkurrenzfähige und stabile Alternative sein. Diese Arbeit führt einen neuen experimentellen Aufbau zur Untersuchung der DOE, einer Dreiphasenreaktion, ein. Der Aufbau besteht aus einer in-line Gasabsorptionskolonne und einem Festbettreaktor. Mit dieser Konfiguration konnten die unterschiedlichen Massentransferphänomena getrennt untersucht werden. Mittels Gasabsorptionskolonne kann der gas/flüssig Stoffdurchgang (Gaslöslichkeit) eingestellt werden und der gas/fest Stoffdurchgang (Filmdiffusion) kann mit dem Volumenfluss eingestellt werden. Es wurde ermittelt, dass die Porendiffusion eine wichtige Rolle für die Reaktion spielt, die durch die geringe Konzentration von gelöstem Sauerstoff vermittelt wird. Daher sollte der Partialdruck erhöht werden, was die Raumzeitausbeute wegen des HENRY-Gesetzes erhöht. Eine maximale Reaktionsrate wurde oberhalb von 4 bar Sauerstoffpartialdruck gemessen, während die Temperatur konstant bei 50 C belassen wurde. Diese Ergebnisse wurden in einem Vergleichssystem erzielt, dem Rührkesselreaktor. Ebenso wurde der Einfluss der Struktur des eingesetzten Katalysators und insbesondere des Trägers untersucht. So wurde festgestellt, dass mikroporöse Träger fast keinen Umsatz zeigten, wohingegen meso- and makroporöse schon. Dies unterstreicht die Bedeutung der Porendiffusion. Für die Diffusionsimprägnierung konnte der Schluss gezogen werden, dass eine geringe Konzentration des Metallsalzes und eine kurze Imprägnierdauer zu leistungsfähigeren Katalysatoren führen. Analysen mit einer Elektronenmikrosonde zeigten ebenso, dass das imprägnierte Gold näher am Rand der Trägerkügelchen gefunden werden konnte. Abschließend wurde die Desaktivierung erforscht, die schneller auftritt, wenn die Metallbeladung verringert wurde. Verschiedene Gründe konnten erfolgreich ausgeschlossen werden, welche am Ende zum Hinweis führten, dass Methacrylsäure oder oligomere Spezies die reversible Desaktivierung verursachen.
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    Distinct specificities of the HEMK2 protein methyltransferase in methylation of glutamine and lysine residues
    (2024) Weirich, Sara; Ulu, Gizem T.; Chandrasekaran, Thyagarajan T.; Kehl, Jana; Schmid, Jasmin; Dorscht, Franziska; Kublanovsky, Margarita; Levy, Dan; Jeltsch, Albert
    The HEMK2 protein methyltransferase has been described as glutamine methyltransferase catalyzing ERF1-Q185me1 and lysine methyltransferase catalyzing H4K12me1. Methylation of two distinct target residues is unique for this class of enzymes. To understand the specific catalytic adaptations of HEMK2 allowing it to master this chemically challenging task, we conducted a detailed investigation of the substrate sequence specificities of HEMK2 for Q- and K-methylation. Our data show that HEMK2 prefers methylation of Q over K at peptide and protein level. Moreover, the ERF1 sequence is strongly preferred as substrate over the H4K12 sequence. With peptide SPOT array methylation experiments, we show that Q-methylation preferentially occurs in a G-Q-X3-R context, while K-methylation prefers S/T at the first position of the motif. Based on this, we identified novel HEMK2 K-methylation peptide substrates with sequences taken from human proteins which are methylated with high activity. Since H4K12 methylation by HEMK2 was very low, other protein lysine methyltransferases were examined for their ability to methylate the H4K12 site. We show that SETD6 has a high H4K12me1 methylation activity (about 1000-times stronger than HEMK2) and this enzyme is mainly responsible for H4K12me1 in DU145 prostate cancer cells.
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    Chitin/cellulose blend fibers prepared by wet and dry‐wet spinning
    (2020) Ota, Antje; Beyer, Ronald; Hageroth, Ulrich; Müller, Alexandra; Tomasic, Patricija; Hermanutz, Frank; Buchmeiser, Michael R.
    We describe the wet and dry‐wet spinning of multifilament cellulosic composite fibers, namely chitin/cellulose fibers. The direct solution process for the two biopolymers based on an ionic liquid as solvent represents an environmentally friendly and alternative technology to the industrially applied viscose and lyocell process. Both cellulose and chitin possess good solubility in 1‐ethyl‐3‐methylimidazolium propionate ([C2C1Im][OPr]) and were spun into multifilament composite fibers. Moreover, for the first time, pure chitin multifilament fibers were obtained by dry‐wet spinning. The effect of chitin addition on the filament properties was investigated and evaluated by microscopic, spectroscopic, and mechanical analyses.
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    Influence of In‐doping on the structure and electrochemical performance of compositionally complex garnet‐type solid electrolytes
    (2025) Alsawaf, Alaa; Karkera, Guruprakash; Diemant, Thomas; Kante, Monaha Veerraju; Schneider, Yannik; Velasco, Leonardo; Bhattacharya, Subramshu S.; Stainer, Florian; Wilkening, Martin; Clemens, Oliver; Janek, Jürgen; Hahn, Horst; Botros, Miriam
    The electrochemical instability of electrode active materials as well as the flammability of the organic liquid electrolytes in Li‐ion batteries pose challenges for their safety and long cycle life. Solid electrolytes (SEs) that exhibit high ionic conductivity and a wide electrochemical stability window alleviate these challenges. Garnet‐type Li7La3Zr2O12 is a promising SE for next‐generation all‐solid‐state batteries. Herein, samples are prepared via a modified solid‐state reaction of compositionally complex Li6.3+zLa3Zr1.1-z Nb0.8Gd0.1InzO12 under different sintering atmospheres. X-ray diffraction patterns and Raman spectra prove the formation of a cubic garnet structure. Significant morphological changes are detected upon In‐doping and correlated to the ionic conductivity. The total Li‐ion conductivity of the dense pellets reaches 1 mS cm-1, among the highest reported to date, with an activation energy of 0.38 eV for the macroscopic ion transport obtained by impedance spectroscopy and as low as 0.24 eV for local Li‐ion hopping processes determined by 7Li nuclear magnetic resonance spin‐lattice relaxation measurements. The electronic contribution to the conductivity is negligible (10-10 S cm-1) making this compositionally complex SE a suitable candidate for all‐solid‐state battery applications.